Improvement in centrifuge rotors



A. U- AYRES IMPROVEMENT IN CENTRIFUGE ROTORS Original Filed Feb.- 27,1958 Jan. 29, 1963 3 Sheets-Sheet 1 ms mm 2 N Mu M3 m 5 B N Q w m 4 i OA I M. 2 M M B \\v ATTORNEY A. U. AYRES Jan. 29, 1963 INVENTOR. ARTHURu. AYRES BY U a s ATTORNE Jan. 29, 1963' A. u. AYRES 3,075 5 IMPROVEMENTIN CENTRIFUGE ROTORS Original Filed Feb. 27, 1958 3 Sheets-Sheet 3 W I 036 f INVENTOR. ARTHUR U. AYRES ATTORNEY United States Patent 3,075,65IRZFRQVEWiENT EN (JEN'ERHFUGE RGTGRS Arthur U. Ayres, Philadelphia, Pa,assignor to The fihwples Qorporation, a corporation of Delaware Griginalapplication Feb. 27, 1953, her. No. 718,634, new

Patent No. spaaasa, dated Get. 20, 1961. Divided and this applicationMar. 6. 1959, fier. No. 797,792

2 Qiaims. (Cl. 233-- i-6) This application is a division of myco-pending application now Patent No. 3,004,050, issued October 10,1961.

This invention pertains to a centrifuge rotor for the refining of fattyoils (e.g. glyceride oils), and more particularly to a centrifuge rotorfor the refining of vegetable and animal oils, such as cottonseed oil,soya bean oil, peanut oil, corn oil, sunflower seed oil, sesame oil,rape seed oil, cocoanut oil, babassu oil, palm oil, palm kernel oil,linseed oil, tallow, lard, grease, fish oil, whale oil, etc.

Fatty oils are ordinarily refined by treating the same with an aqueousalkaline reagent, such as sodium carbonate and/or sodium hydroxide. Thisis followed by the separation of the refined oil from the aqueous phase,the latter containing reaction products and/or impurities such assoapstock, gums, and/or color bodies. The purpose of such refining is toneutralize and remove free fatty acids, to remove gums, to remove colorbodies and/or to otherwise improve the quality of the oil.

Such refining, particularly when the purpose is to remove free fattyacids, is frequently followed by a second refining known in the art asrerefining. The purpose of rerefining is to further improve the qualityof the oil, largely by way of removal of color bodies, for which areagent comprised of aqueous caustic soda is well suited.

The use of a rerefining step is generally accepted practice when aqueoussodium carbonate is employed as the reagent for neutralizing free fattyacids in the initial refining, for sodium carbonate is rather deficientas a reagent for removing color bodies. The use of a rerefining step isalso beneficial in many instances, depending on the source and/ or typeof the crude oil, when the initial refining is conducted withstoichiometric or near stoichiometric proportions, based on free fattyacid present, of caustic soda as the refining reagent.

In any event, the residue of free fatty acids remaining in the fatty oilalter initial refining with an alkaline reagent to remove free fattyacids is very low, e.g. below 25%. Fatty oils so refined also are low inmaterials commonly referred to as gums, e.g. phosphatides, proteinsceousmaterials, resins, etc. Fatty oils which have been degummed otherwisethan by treatment with a reagent to remove free fatty acids also are lowin gum-s. Also certain fatty oils are initially low in free fatty acids,e.g. below 1%.

In the treatment of such fatty oils which are low in free fatty acidsand/or gums, whether in such state naturally or as a result of priorprocessing, it is common practice to employ a reagent, such as aqueouscaustic soda, to improve the quality of the oil, e.g. by reduction infree fatty acids and/or col-or or otherwise. In such practic a smallamount of soapstock is usually formed, whether by reduction in freefatty acids, or by saponification of a small amount of neutral oil, orboth, and the aqueous caustic soda reagent solutions employed arefreqaently of such concentration as to cause the soapstock 3,75,fid5Patented Jan. 29, 1963 formed to be salted out from the aqueous reagentphase, or to otherwise appear in whole or in part in the form of a thirdphase separate from the oil and the aqueous reagent phase. The result isthat the soapstock, being of a density intermediate that of the fattyoil and that of the aqueous phase, tends to be discharged from thecentrifuge along with the fatty oil. This is because the aqueous phase,being of a density greater than that of the soapstock phase, forms alayer in the bowl in a position radially outwardly from the soapstocklayer, and thus interferes with the proper discharge of the soapstocklayer from the bowl as a heavier phase. As a result, at least a part ofthe soapstock is forced to discharge from the bowl as a lighter phase,ie along with the oil, thus defeating the purpose of the operation,which is to separate both soapstock and aqueous reagent phase from theoil.

This condition may be alleviated, at least to some extent, by theseparate feed of water into the peripheral zone of the bowl to reducethe concentration of caustic soda in the aqueous phase, with consequentreduction in its density, ideally to a point where the density of theaqueous phase becomes the same as that of the soapstock phase. Underideal or near ideal conditions, both phases then are discharged from thebowl together, and separately from the oil. The dilution of the aqueousphase, however, results in the formation of a certain amount ofoil-containing aqueous emulsion which is discharged from the bowl alongwith the soapstock and aqueous phases, with consequent loss in oil.

Another source of difficulty resides in the fact that the capacity ofthe soapstock phase to retain aqueous reagent phase, either by solutionor entrainment, varies not only between different oils, but also for anygiven individual oil depending in large measure on its gum content. Evenduring a given run there may be Variations to the extent that a separateaqueous layer may form only sporadically, or may disappear sporadically.In any event, it is difiicult to continuously centrifugally separate byliquid balance an aqueous reagent phase as a layer separate from thesoapstocl; layer, and to continuously discharge the same from the bowl,e.g. over a weir.

Af er extensive experimentation, I have discovered and perfected acentrifuge rotor or bowl for the refining of fatty oils wherein theaqueous phase, if, when and to the extent occurring as a layer separatefrom the soapstock layer, is separated and separately discharged fromthe centrifugal bowl, while leaving the oil and soapstock layers indesired hydrostatic balance.

Furter features of the invention will become apparent to persons skilledin the art upon becoming familiar herewith, and as the specificationproceeds, and upon reference to the drawings in which:

FIGURE 1 is a vertical section, shown broken, illustrating apparatusembodying and useful in the practice of the invention;

FIGURE 2 is a section taken generally on line 2--2 of FEGURE l, withportions removed for better illustration; and

FIGURE 3 is an enlargement of a portion of FIG- URE 1.

Referring now more particularly to the drawings, the centrifuge rotorlib is shown provided with an inlet feed boss 11 which is surrounded bya guide bushing assemably or drag 12. The guide bushing assembly 12 isse- 3, cured in position on a base 13 which also carries a feed nozzle 1through which the reaction mass is continuously fed into the centrifugerotor 10.

In the apparatus as illustrated, an auxiliary feed nozzle 15 also issecured to the base 13, and surrounds the feed nozzle 14, and feednozzle 14 is shown provided with a circumferential head 16, the purposeof which is to deflect outwardly against the inner wall of boss 11 anyliquid fed into the bowl through the nozzle 15 in the practice of amodification of the inventionv to be hereinafter more particularlydescribed.

The lower end 17 of rotor is provided with a cylindrical flange 18positionedfinteriorly of the rotor. The upper .end of flange 18 forms a.seat for a flange 20 of a feed directing member 19 shown with a conicalbase portion. Member 19 may be secured in position on flange 18 by anysuitable means, such as welding, Flange 18 is provided with a pluralityof circumferentially spaced slots illustrated at 21, in order to aifordoutlets from the space between thernember 19 and the inner peripheralbottom, portion of the rotor .for liquid fed into and passing upwardlyand outwardly through such space.

I Member 19, asrshown,v is provided on its inner conical surface with aplurality of circumferentially spaced radially extending vanes or fins28, and similarly on its outer conical surface with a plurality ofcircumferentiallyspaced radially .extendingvanes or line 36. The fins 28'extend'inwardly toward feed opening 29 in the lowermost part of themember 19. Pins 30 extend from the'outer surface of the membcr19 to theinner surface of the lower end 17 ofthe rotor.

The construction so far particularly described may be regarded as moreor less conventional, and well-known.

Referring now to the upper part of rotor 10, at 31 is showna rotor topwhich threadedly engages the upper interior of rotor 10 as illustratedat 32. Rotor top 31 includes an upwardly extending center portion 33shown provided with'threads' 34 for-engagement by a nut on an overheaddriving spindle, not shown.

An annular member 35 threadedly'engages rotor top 31 as illustrated at36, and is provided with an upwardly extending cylindricalportion 37which is threadedly engaged by a, ring darn nut SSIas illustrated at 39,ring dam 42' being secured in position between cylindricalportion 37 andring dam nut 38.

Member 35 also is provided with an annular recessed.

portion 43 in which is positioned an annular resilient valve member 44-shown, associated with a plurality of circumferentiallyspaced verticaloutlet channels 45 milled intothe interiorwall of rotor 10.

In the operation or" the apparatus shown in the drawings, a stream ofthe reaction mass is projected through nozzle l l up into rotor 16'through feed opening 29, and is brought up to rotational speed with theassistance of fins723, and circumferentially spaced radially extendingvanes 27.' By virtue of centrifugal'force, the reaction.mass isseparatedinto layers arranged in order of decreasing density in aradially inward direction from the interior peripheral wall of rotor 10.

In the following particular description which is by way oi" example, itwill beassumed that the reaction mixture is comprised of fatty oil,'soapstock' and aqueous caustic soda having a density greater than thatof the soapstock.

Undcr the influence of centrifugal force, the aqueous electrolyte phase,being the heaviest phase, builds up on the interiorwall of rotor 10, andflows toward annular recess 43, through a plurality of circumferentiallyspaced channels 49 in rotor top 31.

Annular valve member 44 is so chosen as to have a density intermediatethat of the soapstock phase and the aqueous electrolyte phase, and maybeef any'suitable resilient material, such as rubber, natural orsynthetic; capable of" increasing and decreasing in diameter,

i.e. in radial distance from the axis of rotation,,under the appliedconditions present.

Valve member 44 is conveniently, though not necessarily, circular incross section, and its density may be varied to suit requirements by anymeans known in the art, e.g. ranging all the way from being made hollowto being loaded with various powdered substances, including metals,which may be incorporated in the rubber itself, or placed in a hollowinterior, or built in as a core, as will be readily understood bypersons skilled in the art.

it will be understood that when rotor 10 is empty, or when the aqueouselectrolyte phase does not form a layer separate from the soapstock,annular valve member 44 is expanded in radius, i.e. increased incircumference, by;

the applied centrifugal force so as to close vertical outlet channels45, for the density of member 44 is so chosen as to be greaterthan thatof the soapstock layer.

Upon the appearance, however, of a third layer comprised of aqueouselectrolyte which, under the conditions assumed above, is of greaterdensity than the valve member 44, such aqueous electrolyte layer willflow upwardly along the-interior wall of rotor 10 into annular recess43, whereupon annular valve member 44 will decrease in radius (i.e. incircumference) by virtue of floating in, or, in other words, beingdisplaced inwardly by, the heavier aqueous electrolyte layer whichescapes from the bowl through outlet channels 45.

Thus as long as an aqueous electrolyte layer is present in the rotor, itwill be discharged from the rotor through channels 45; Soapstock, on theother hand, will not be discharged through channels 45, for when anaqueous ei'ectrolyte layer is not present, channels 45 are closed byvirtue of the radial expansion of circumferential valve member 44 duetocentrifugal force, such expansion being possible in the presence ofsoapstock only, for valve member 44 is of greater density than thesoapstoclc.

From the foregoing it will be seen that when an aqueous; electrolytelayer is present in rotor 19, irrespective of the'manner in which it mayoccur, e.g. intermittently and/or varying in volume, it-is'carried oiffrom the rotor 19' Without interfering with the separation of soapstockfrom oil;

. Oil and soapstock are separated from each other in rotor--10, and aredischarged therefrom, in any desired manner;

As illustrated,'rotor top 31 is provided with a conventionaldividing-disc 45,- around the inner circumferential edge 47 of'which theseparated oil escapes upwardly, and around the outer-cir cumferentialedge 48 of which the soapstock escapes upwardly.

' The oil flows upwardly through a plurality of circumfcrentially spacedcircular channels 49 in rotor top 31, and into a pluralityof-circumferentially spaced channels 52 formed between longitudinalgrooves 53 in portion 33' and-a sleeve-54'surrounding portion 33. Theoil escapes overupper edge 55- of sleeve 54, and is collected in anyconvenient manner such as by use of a rotor cover, not shown. Sleeve 54may be attached to'rotor top 31 in any desired manner, such asbywelding.

' Separated soapstock escapes upwardly around'the circumferential edge-48 of disc 4-6, and passesupwardly through circumferentially spacedchannels 56, area 57,

I and over the inner circumferential edge of ring dam 42,

escaping outwardly through a plurality of circumferentially spacedoutlet ports 53. As shown, the soapstock, on escaping from ports 53, isdeflected downwardly by hood 59, and may be collected along with aqueouselectrolyte escaping through channels 45, in any suitable manner such asby the use of a rotor cover, not shown. On the other hand, soapstock andaqueous electrolyte may be collected separately, if desired, as will beobvious. From the foregoing particular description it will be seen that,in the practice of the invention, disturbances in the separationot'soapstock from the oil'due to the forma tion of a third layercomprised of aqueous electrolyte, are eliminated, for if, when and assuch aqueous electrolyte layer forms, it is automatically andselectively removed from the zone of centrifugal separation throughoutlets separate from those for the discharge of oil and soapstock, thuspermitting the separation of soapstock from the oil to proceed in anormal Way.

Priming of the centrifuge bowl upon start-up may be efiected in anydesired or customary manner, in the present instance, preferably with aliquid of lower density than valve member 44, so as to keep channels 45closed during priming and to cause priming liquid to discharge over ringdam l2, as will be well understood by persons skilled in the art. Anysuitable priming liquid may be employed, e.g. water, or an aqueoussolution of electrolyte, such as of caustic soda or sodium carbonate.

As is well known in the art, the ease with which soapstocl; may bedischarged from a centrifugal rotor may vary widely from oil to oil andwith the conditions under which the oil is refined. Certain conditionsof refining, for instance, may reduce the fluidity of the soapstockquite materially. Moreover, the tendency of soapstock to stick to therotor wall also may vary from oil to oil and with the conditions ofrefining. In overcoming such difficulties, the present invention lendsitself ideally to the floating of the soapstock layer through the rotoron the surface of a heavier aqueous electrolyte layer, withoutinterfering with the separation of the soapstock from the oil by liquidbalance under the conditions employed in the zone of centrifugation, orthe discharge of the separated oil and soapstock layers from the rotor.Such floating of the soapstock layer on a heaviest aqueous electrolytelayer takes place in the practice of the invention whenever suchheaviest layer appears.

To assist in such discharge of soapstock from the rotor, a suitableauxiliary liquid of higher density than the soapstock, such as aqueouselectrolyte, may be passed upward- 1y through the annular space affordedbetween the nozzle 15 and the nozzle 14 shown in FIGURE 1 of thedrawings. This liquid impinges against the head 16 formed on the nozzle14 and is deflected into contact with the inner wall of the boss 11 ofthe rotor 14 The centrifugal force generated by the rotation of therotor causes the liquid to cling to this surface and to flow upwardlyinto the space occupied by the radially extending fins 3%. Pins 36 bringthe liquid up to the speed of the rotor, and the liquid is impelledoutwardly through openings 22 under the influence of centrifugal force.Liquid impelled through the openings 21 fiows upwardly along the innerwall of the rotor 16*, thus forming a continuously moving liquid layerupon which the soapstock floats as it passes upwardly through the rotor.Sticking of the soapstocl; to the interior wall of the bowl and/ orpacking of the soapstock thereon are thus avoided.

The flotation liquid, being of higher density than the soapstock, isdischarged from the rotor through channels 45, the same as the aqueouselectrolyte layer is discharged when formed in the rotor as aboveparticularly described. Rubber ring or valve member 44 is, of course,chosen as to density to permit the discharge of the flotation liquid,but not of soapstock.

Vhen the refining or rerefining is under conditions, e.g. including thesource of the oil, such that a third layer comprised of aqueouselectrolyte is formed, or is likely to form, in the rotor, such asintermittently or continuously, the flotation liquid, if employed, ispreferably though not necessarily of the same or similar density as suchaqueous electrolyte layer, and preferably though not necessaril also ismiscible therewith.

However, it is conceivable that, even though water has a densityslightly less than that of the usual soapstock, it might be fed into therotor as a flotation liquid when the formation of a separate layer ofaqueous electrolyte phase is assured, whereupon the water may mere- 1ymix with the latter layer to increase its volume with some decrease indensity, but preferably not closely approaching that of the soapstock,in order that valve member 44 may function in its intended manner.

On the other hand, aqueous caustic soda and/ or aqueous solutions of itssalts, such as of sodium carbonate or of sodium sulfate, or aqueoussolutions of any other suitable electrolyte, may be employed as theflotation liquid, if of higher density than soapstock, or if capable ofmixing with separated aqueous electrolyte to form a final flotationliquid of higher density than the soapstock, so as to make possible itsselective discharge from the rotor through the channels 4-5.

The following examples are given by way of illustration and not oflimitation.

Example 1 Degummed soya bean oil having a free fatty content of 0.25% byweight was continuously mixed at a rate of 2500 pounds per hour with1.42% of its volume of aqueous caustic soda of 14' Be. at a temperatureof 8-0" F. The stream of mixed oil and aqueous caustic soda was thenheated to 140 F. and the stream was then centrifugally separated in acentrifuge having a rotor of the type shown in the drawings. A separatelayer of aqueous caustic soda began to form immediately in the rotor,and it was discharged peripherally therefrom, that is through channelssimilar to the channels 453. The soapstock was discharged over a ringdam corresponding to ring dam 42. A composite sample of the soapstocltupon analysis showed that it was of very low oil content, namely 2.04%by weight on a dry basis. The separated oil was bright throughout therun showing that it was extremely low in soap content.

Example 2 Degummed soya bean oil having a free fatty acid content of0.45% by weight was continuously mixed at a rate of 2500 pounds per hourwith 2.68% of its volume of aqueous caustic soda of 12 as. at atemperature of F. The stream of mixed oil and aqueous caustic soda wasthen heated to P1, and the stream was then subjected to centrifugalseparation in a centrifuge having a rotor similar to the rotor shown inthe drawings, but with valve member 44 and channels 45 omitted. Therewas no discharge of separated heavy component for about 20 minutes,whereupon soapstock (a composite heavy layer) began to be discharged.The separated oil was bright initially and relatively soap free, butgradually became more and more muddy with entrained soap. In about 35minutes after the run started there was a sudden heavy discharge ofsoapstock, whereupon the discharged oil cleared up and becarne brightagain. A number of such surges or sudden heavy discharges of soapstockoccurred with similar variations in the character of the separated oil.A composite sample of the soapstock was analyzed, and showed an oilcontent of 10.6% by weight on a dry basis. A composite sample of therefined oil showed that it was relatively high in soap content.

Example 3 In an effort to rectify the unsatisfactory refining conditionsexemplified in Example 2, degummed soya bean oil having a free fattyacid content of 9.66% by weight was continuously mixed at a rate of 2503pounds per hour with 0.72% of its volume of aqueous caustic soda of 22Be. at a temperature of 80 F. The stream of mixed oil and reagent wasthen heated to 140 F., and the stream was then continuously separated ina centrifuge having a rotor similar to the rotor shown in the drawings,except that the valve member 34 and the channels were omitted. 7.5% byvolume of water, based on the total volume of'the reaction mass, was fedinto the rotor of the centrifuge through a feed nozzle having aconstruction and arrangement similar to that disclosed at 15 in FIGURE 1of the drawings, the water being continuously deposited on however,showed that it contained 29.4% of oil on a dry basis, which represents arather high loss in oil.

From the foregoing description it will be seen that the annular edge 47operates as a weir over which the lightest layer, e.g. refined vegetableoil, is discharged. It alsowill be seen that annular edge 47 controlsthe depth of liquid in the bowl,'for it is not possible for liquid tobuild up in the bowl between the axis ofrotation'and the annular edge47.

The annular inner edge of ring dam 42 also operates as a weir over whichthe next heavier layer, i.e. the layer of intermediate specific gravityor density, e.g. soapstock, is discharged from the bowl. The radialdistance from the axis of rotation to the annular inner edge of ringdam42 controls the radial position of the dividing line or interface in thebowls separatory space between the lightest layer and the next heavierlayer. The radial position of such interface is made adjustable bymaking ring dam 42 interchangeable, and providing a variety of ring damswith annular inner edges of dilferent radial distances from I the axisof rotation. In any event, such interface is made to fall betweenannular edge 4-7 and annular edge 48 when the bowl is in operation. Forany given sizeof ring dam 4-2, the radial position of the interface ordividing line between the lightest layer and the next heavier layer isdependent upon their relative specific, gravities.

In the case of the refining or rerefining of fatty oils, it is customaryto select a ring dam 42 with the radial distance from the axis ofrotation to its inner operative edge such as to bring the interface ordividing line between the lightest and next heavier layers as close toannular edge 48 as is practicable, without possible loss of oil overweir 48 due to possible variations in conditions within the bowl. avolume of oil in the bowl as is reasonably possible during separation,thus increasing the resident time during which any portion of the oil isundergoing treatment for the separation of reaction products and reagenttherefrom. The dividing line or interface, however, may occupy any otherposition between annular edges 47 and 48, as desired.

It is the disturbance of the hydrostatic balance between the lighter andnext heavier layers due to the appearance of a third layer, whetherintermittent or continual, that has heretofore presented a major problemin the refiningof fatty oils, and particularly fatty oils of low freefatty acid and/or gum content, whether previously refined or not.

It is the removal of the heaviest layer from the bowl, as, if and whenit appears, that produces the new and unexpected results which fiow fromthe practice of the invention, for it is by effecting such removal ofthe heaviest layer that the desired hydrostatic balance between thelighter and the next heavier layers is maintained in undisturbedcondition. Since the heaviest layer may appear only intermittently, andmay vary considerably in volume, or if appearing continuously, may stillvary in volume during the separation, it is by the discharge of thisheaviest layerfro-rn the periphery of the bowl under control ofdifference in densities, that makes possible the desired high efiicientseparation of refined oil from reaction products and reagent. The termslight, heavy, and intermediate may obviously respectively replacelighter, heaviest, and next heavier as referring to the layers herein.

While the invention has been described more partie ular-ly in connectionwith the rerefining of fatty oils, it is to be understood that it isapplicable to the initial refining of fatty oils under conditions suchthat a third layer of The purpose is to keep as largeaqueous-electrolyte is likely to appear. Also while the appearance of athird layer comprised of aqueous electrolyte' occurs more often whencaustic soda is employed as the alkaline refining agent, the samesituation is capable of occurring when other alkaline refining reagents,such as sodium carbonate, are employed in excess.

In the practice of the invention, the concentration of alkaline refiningreagent in the aqueous solution employed employed vary widely from plantto plant and are such as to causethe appearance of a third layer in thebowl, if the aqueous reagent solution is employed in sufficient excessto create this condition. It may be expected, however, that with thesame percentage excess of aqueous refining solution over that requiredto neutralize free fatty acids, the appearance during the separation ofa third layer is more likely to occur with aqueous solutions of higherBaum. Generally-speaking, such third layer does not appear when thealkaline refining agent is substantially depleted during thetreatment,e.g. in the case of aqueous causticsoda, to below a specificgravity equivalentto that of 12 B.

The temperatureat which the process is practiced also. is not critical,forthe invention isoperable irrespective.

it will be understood thatthe invention provides a,

safety measure guarding against disturbingthe hydrostatic balancebetween the fatty oil and soapstock or other reaction productsbythepossible appearance .of a third layer comprised of aqueouselectrolyte.

While the .valve member 44 has been more particularly described asarubber ring, this is by way of illustration, for valve member 44 may beof any other suitable material of appropriate specific gravityintermediate that of the heavier and heaviest layers.

Moreover, while the centrifugal bowl has been illustrated forconvenience in the drawings as being of tubular shape, and as havingwings. serving as an acceleratingdeceleratingdevice, it is to beunderstood that the centrifuge bowl may have any other configuration andcon-. struction without departing from the spirit of the invention. Thusthe invention is equally adaptable to what is known as the disc-typebowl, and to bowls of any other type.

Having described my invention, it is to be understood that this isby wayof illustration, and that changes, omissions, additions, substitutionsand/or other modifications,

may be made without departing from the spirit thereof. Accordingly it isintended-that the patent shall cover by suitable expression in theclaims the. various features of patentable novelty that reside in theinvention.

1 claim:

-1. In a centrifuge rotor for the separationof immiscible componentsadapted to stratify into light, heavy and intermediate layers,respectively, the rotor having a weir spaced inward from .the outermostportion of the rotor and over which such light layer may be discharged,having a second weir outward-from the first weir and over which suchintermediate layer may be discharged, and having an opening through thewall of the rotor at its periphery to the outside thereof; theimprovement of a valve element comprising an annulus disposed about theinside of the rotor adjacent its periphery'and substantially in the sameradial plane as said opening and being selected of resilient material ofdensity intermediate that of such heavy and intermediate layers to bepressed outward under centrifugal force to cover the opening in theabsence of such heavy layer and to float inward on such heavy layeragainst substantially the same degree of centrifugal force when suchheavy layer is in the rotor to permit escape through the opening of suchheavy layer only and tothereby avoid 9 10 disturbance by such heavylayer of. the hydostatic balance 1,232,104 Sharples July 3, 1917 betweenthe light and the intermediate layers. 1,373,743 Jones Apr. 5, 1921 2..The centrifuge rotor of claim 1 having an inlet lead- 1,534,604 Ter MeerApr. 21, 1925 ing to the inner periphery of the rotor for the feed of an1,981,800 Calkins Nov. 20, 1934 auxiliary liquid into said rotor. 52,138,468 Ayres Nov. 29, 1938 2,209,554 Bath July 30, 1940 ReferencesCited In the file of this patent 2,577,326 Harstick et a1 Dec. 4, 1951UNITED STATES PATENTS 2,628,021 Staafi Feb. 10, 1953 1,201,558 Cobb Oct.17, 1916 2.712.896 Boldrin July 12, 1955

1. IN A CENTRIFUGE ROTOR FOR THE SEPARATION OF IMMISCIBLE COMPONENTSADAPTED TO STRATIFY INTO LIGHT, HEAVY AND INTERMEDIATE LAYERS,RESPECTIVELY, THE ROTOR HAVING A WEIR SPACED INWARD FROM THE OUTERMOSTPORTION OF THE ROTOR AND OVER WHICH SUCH LIGHT LAYER MAY BE DISCHARGED,HAVING A SECOND WEIR OUTWARD FROM THE FIRST WEIR AND OVER WHICH SUCHINTERMEDIATE LAYER MAY BE DISCHARGED, AND HAVING AN OPENING THROUGH THEWALL OF THE ROTOR AT ITS PERIPHERY TO THE OUTSIDE THEREOF; THEIMPROVEMENT OF A VALVE ELEMENT COMPRISING AN ANNULUS DISPOSED ABOUT THEINSIDE OF THE ROTOR ADJACENT ITS PERIPHERY AND SUBSTANTIALLY IN THE SAMERADIAL PLANE AS SAID OPENING AND BEING SELECTED OF RESILIENT